feat: add blog system with static site generator

- Add blog posts in Markdown (_posts/)
- Build script converts MD to HTML at container build time
- First posts: building with AI lessons, quick start guide
- AGENTS.md documents blog writing style (unixsheikh-inspired)

www/AGENTS.md

@@ -0,0 +1,120 @@
+# DearDiary Website & Blog - Agent Instructions
+
+## Overview
+
+The DearDiary website is a static HTML site generated from Markdown blog posts. No frameworks, no build complexity.
+
+## Structure
+
+```
+www/
+├── _posts/           # Blog posts in Markdown (source)
+│   └── YYYY-MM-DD-slug.md
+├── blog/             # Generated HTML (don't edit manually)
+│   ├── index.html
+│   └── YYYY-MM-DD-slug/
+│       └── index.html
+├── css/
+│   └── styles.css
+├── docs/             # Documentation (also static HTML)
+├── js/
+│   └── main.js
+├── index.html        # Main website (uses envsubst for templating)
+├── build-blog.js    # Blog generator script
+└── package.json     # npm deps (gray-matter for parsing)
+```
+
+## Building
+
+```bash
+cd www
+npm install
+node build-blog.js
+```
+
+This converts `_posts/*.md` → `blog/*.html`.
+
+## Blog Post Format
+
+Frontmatter:
+```yaml
+---
+title: Your Post Title
+date: 2026-03-27
+author: Konrad Lother
+excerpt: One sentence summary for the blog index
+---
+```
+
+## Tone & Style Guide
+
+Read unixsheikh.com for inspiration. Key characteristics:
+
+### Voice
+- **Direct and authoritative** - Say what you mean, don't hedge unnecessarily
+- **Personal opinion is welcome** - Write from a first-person perspective
+- **Technical but accessible** - Explain complex topics simply
+- **Not afraid to be contrarian** - Challenge conventional wisdom when you disagree with it
+
+### Structure
+- **Strong opening** - Hook the reader immediately
+- **Clear sections** - Use headers to organize thoughts
+- **Concrete examples** - Illustrate abstract concepts
+- **Practical takeaways** - End with actionable advice
+
+### What to Avoid
+- Corporate/tech-blog speak ("leverage", "synergy", "cutting-edge")
+- Unnecessary hedging ("might", "could potentially", "in some cases")
+- Padding or fluff - every sentence should add value
+- Being mean-spirited - critique ideas, not people
+
+### Example Openers
+
+Bad:
+> "In today's fast-paced digital world, journaling has evolved..."
+
+Good:
+> "Traditional journaling apps ask you to write long entries at the end of the day. But let's be honest - who has time for that?"
+
+### Length
+- 500-1500 words is ideal
+- If you're writing more, consider splitting into multiple posts
+- Short posts can be 200-300 words if the idea is complete
+
+## Topics to Cover
+
+### DearDiary-Specific
+- How to use features effectively
+- Tips and tricks for better journaling
+- Behind-the-scenes development stories
+- Why AI-assisted journaling makes sense
+- Privacy and self-hosting benefits
+
+### General Tech Thoughts
+- Software craftsmanship
+- Human-AI collaboration
+- Simplicity in development
+- Critical thinking about tech trends
+- The value of boring technology
+
+### Personal/Philosophy
+- Productivity and reflection
+- Memory and identity
+- The importance of记录 (record-keeping)
+- Learning from daily life
+
+## Post Ideas
+
+1. Why capture events, not essays (the thesis behind DearDiary)
+2. My journaling experiment - 30 days of DearDiary
+3. What I learned building an app with AI
+4. The case for boring technology in side projects
+5. How to remember your life better
+6. Self-hosting isn't hard, it's just unfamiliar
+
+## Technical Notes
+
+- The `build-blog.js` uses a simple regex-based Markdown converter
+- For full Markdown support (tables, footnotes), consider using a proper parser
+- Images should be hosted externally or added to the repo
+- Code blocks work but syntax highlighting is limited